Process for selective extraction of nitrates from aqueous nitrate-sulfate solutions



Patented Oct. 4, 1960 PROCESS FOR SELECTIVE EXTRACTION F NI- TRATES FROMAQUEOUS NITRATE-SULFATE SOLUTIONS Charles T. Dickert, Levittown, andAlbert F. Preuss, Jan,

Hatboro, P31. assignors to Rohm & Haas Company, Philadelphia, Pa., acorporation of Delaware No Drawing. Filed Mar. 20, 1957, Ser. No.647,182

Claims. (Cl.,23,..-14.5)

This invention relates to a process for selectively extracting nitratesfrom aqueous nitrate-sulfate solutions.

A principal object of the invention is to make possible the recovery andre-use of expensive nitrates from nitratesulfate solutions. Suchrecovery and re-use is of especial value and importance in the uraniumprocessing industry 'in which it has previously been the practice todiscard of the nitrates by means of a liquid-liquid extraction processutilizing high molecular weight Water-insoluble amines.

Because of the current interest in and importance of :acquiring largequantities of uranium, and further because of the existence of numerouseconomic factors which tend to force the cost upwards, anything whichwill contribute to a lowering of uranium processing costs is of extremeinterest to the industry. Consider, for example, one major process inwhich uranium is leached from its ore by means of sulfuric acid. Theresulting solution is filtered and passed through a column ofion-exchange resin on the particles of which the uranium becomesadsorbed. To elute the uranium from the resin particles a solution ofnitric acid and ammonium nitrate is employed, said solution normallybeing approximately one molar in nitrate. As a result of this elutionessentially all exchange sites (i.e. resin particles which exchangetheir ions for ions in the solution passed through the column) areoccupied by nitrate ions.

Compared to other eluants which might be employed, such as chlorides,the nitrates are quite expensive. Originally, nitrates were chosen overchlorides for this function by uranium processors because of theirgreater uraniumeluting ability and because they are more readilyavailable. Subsequently, another important advantage possessed by thenitrates was discovered when it was found that they removedpolythionates from the ionexchange resin. Polythionate is a poison whichresults when uranium is leached by sulfuric acid and which generally isunaffected when chlorides are employed as the eluant. The value ofremoving polythionates lies in the fact that their presence inion-exchange resins has frequently been found to lead to difiiculty inhydrometallurgical applications of the resin.

Since a considerable volume of ion-exchange resins is employed in eachplant where uranium is being extracted thereby, and elutions withnitrate solutions are frequent, it has been recognized by the uraniumprocessing industry that considerable savings could accrue by recoveringand reusing the nitrates. As an example of the extent of the problem, ina single uranium elution cycle, in which was employed a columncontaining 200 cubic feet of the ionexchange resin, it has been foundthat nitrate losses of from 800 to 1500 pounds are common.

Some of the nitrate eluant, namely that which is in the solutionsurrounding the resin particles and filling the resin interstices, canbe recovered by washing down the resins with water. Some of the nitrateeluant is adsorbed by the resin exchange sites, but some of it isdisplaced by the sulfate in the pregnant leach liquor (resulting fromleaching the uranium ore with sulfuric acid) as more of the latter ispassed through the resin columns. However, the bulk of the nitrate wouldnot be recovered by either of these means and it has b'een proposed thatthis biilk should be recovered by passing fresh sulfuric acid throughthe column. One drawback has been that the resulting solution willcontain both nitric and sulfuric acids. The separating out of the nitricacid from this solution hitherto has been incapable of accomplishment ona sound, economically feasible basis.

One of the ways known to the prior art for separating nitrate fromsulfuric acid solutions was to preciptate out the sulfate with lime. Butthis caused problems in that the uranium eluting solution balance wasupset, an evaporation apparatus and step was required, and an increasedamount of sulfuric acid was made necessary for use in eluting morenitrate from the ion-exchange resin. The use of lime causes anotherobjectionable situation in that a slight excess will bring about theprecipitation of calcium sulfate which will clog the pipelines in acommercial processing plant. Another of the prior art techniques foreffecting this separation, which had an advantage over the one justdescribed in that it made possible the reuse of sulfuric acid, was topass the solution through a column of weakly basic ion-exchange resinsuch as the resin described in US. Patent No. 2,591,574. However, thismethod was objectionable because it required the use of an ammoniarecovery still.

The present invention eliminates the just described and otherobjectionable features of the prior art processes for recoveringnitrates from solutions with sulfuric acid. The improvement consists inselectively extracting nitric acid from such solutions by means of highmolecular weight amines dissolved in a water insoluble diluent, and inaccordance with the steps in the examples to be given later on. By highmolecular weight amines is meant those amines having a molecular weightof at least 185, as represented, for example, by t-dodecylamine. Furtherembraced by the term are primary, secondary, and tertiary amines, andquaternary ammonium compounds.

The unique process was tested and found to work successfully withcompositions such as are found in typical uranium plant conditionswherein the uranium ore is processed as aforesaid, namely by leachingwith sulfuric acid, filtering and adsorbing the uranium on ion-exchangeresins and eluting the uranium with nitric acid-ammonium nitratesolution. At this point, the nitrates were eluted with sulfuric acid.Such a step, as was indicated above, could not have been utilized byuranium processors in the past because it was not known how to separateout the nitrates from the resulting nitrate-sulfate solution on aneconomically sound basis. The ion-exchange resin employed in the columnsor beds was, in this instance, the chloride form of that described inUS. Patent No. 2,591,573, although, of course, many other resins can beused for the same purpose. The resin in the columns was converted to thenitrate form by passing over it the nitrate eluant which conventionallyis used in most commercial plants for eluting uranium which had beenadsorbed by the resin. This eluant consisted of:

0.33 N HNO 0.67 N NH NO 0.50 N (NH SO Enough of this eluant was passedthrough the columns until the efiiuent was found, upon analysis, tocontain no chloride, thus indicating that essentially all the resin hadbeen converted to the nitrate form and the chloride had substantiallyall been'removed therefroml 4 Immediately following the conversion ofthe resin to the nitrate form, sulfuric acid waspassed throughthecolumns as explained above. In one set of experiments sulfuric acid-*wasemployed; in anotherset of; tests a concentration of the acid was used?choice of either one of these concentrations, or'even others, is notmaterial to the present invention; As the percentage of acid isincreased'there is a 'eomparableincrease "in efiiciency of nitraterecovery from the'resin', but workers in the field have to determine theeconomic balance be tween this additionalefficiency on onehand incomparison with the cost of using more acid on the other. When it comesto separating outandrecoveringthe nitrate from the sulfuric acidsolution the present invention appears tofunction' with almost'equalefiijciency atlow or high sulfuric concentrations, aswin be'seen fromdata to be presented'late'rf a H i .The efiluent containing nitrates andsulfuric acid was then treated in accordance warms present invention.

The first, step in the treatment consisted of mixing the' efiiu'ent in aseparatory devicesuch as aseparatory funnel or' a mixer-settler with awater-insoluble amine having a high molecular weight. Any concentrationof amines appeared suitable, but a concentration of 10% weight/ volumeof amine in a kerosene diluent Was employed in most of the tests. Ofcourse, the volume of the extractant employed would vary with the actualamount of amine present." 'Another variable, as may be expected, wasfound to be the ratio of the amount of amine to an equivalent amount ofnitrate, e.g., a 1:1 equivalent ratio of each was found to result in anaverage single stage extractionof approximately 90% of the nitrate,whereas increased amounts of the'amine up to a certain excess (whichamount varies with the amine used) will make possible complete nitrateextraction.

After the ei-fluent and amine were thoroughly mixed together thesolution was allowed to stand until' two layers, 'theorganic and theaqueous, settled out, The aqueous layer, which consists primarily ofsulfuric acid, was'sefaside for further use either to leach uranium fromits ore,"or to elute nitrate from a resin. The next step was'to recoverthe nitric acid adsorbed by the amine. This was done by stripping theacid from'the organic phase with basic'solutions "such as magnesiumoxide, ammonium hydroxide, sodium hydroxide, etc. to form nitratesaltsolution's. The stripping solutions thus pro- -duced were thencapable of further use, after acidification with nitric or sulfuricacid, for elution of'uranium. Thus, the present invention has madepossible a batch wise'process or a complete, practical cyclic processfor recovering" uranium thathas beenleached from its ore with sulfuricacid. With respect to the inventions use as part of a cyclic process, animportant feature is that nitrate solutions used in eluting the uraniumfrom columns of ion-exchange resins'can be almost completely recoveredand reused in further uranium elutions'." Moreover, this recovery ofnitrates from sulfuric acid solutions affords advantages over prior arttechniques in that the uranium eluting solution balanceis not upset: asit is when the sulfate is precipitated out with lime, nor is itnecessary to recover ammonia with all the attendant disadvantages of theextra step and cost involved thereby.

X M LE OF N R TE E VER OMNI: IRA E-SUL T SQLUTIONS U UM. RQQE S N Y MEANOF N- CH NG COLUMNS 7 Following are a number of examples in which thepresent invention was employed to separate nitrates from nitrate-sulfatesolutions collected as efliuents in the ionexchange resin column meansfor processing uranium. To illustrate the scope of the invention, twodifferent representatives of primary, secondary, and tertiary amines,and quaternary ammonium compounds were utilized as the nitrateseparatorandextractant.

PART A.-EL TI OF Nrrnnrn Fnolyr lou Excu-auoe RESIN 'COALUMNS WrrnSULFURICAC I o sash f 9.- s a rwlumnsnha ing. a ne, inch. sside diameterthere was placed 2 09,. m1. of fresh iq gexchange resin, in its chlorideform, of the type disclosed in US. Patent No. 2,591,573. "Two liters ofa n'itrate eluant, consisting of.0.33v N HNO' 0.67 N NH NO and 0.5 'N(NH SQ were passed through the column. The effluent from each" was thentested for chloride and found to be negative. Immediately thereafter 10%H was p sts?! hm h ne. co umn an 2M? 2 04 was p se hrvus th tethe a h; ara e f. 0-3 gaL t-Wmin. fo 3 P r of, tw u s: The. e iue t f om ch lum et h qu h tm. d ermi e whether the itrate a ubs a ial yal e ut d,hislbeins ne y et nn m ing he sntrafionsefihe nit ate and-sul r cfic din fiumber fflu i' ample m. e chfiszlumu When h q s a iq f ul ur capidin h efilu nt w s about equal a h ul u q id. con n ation. n the. eluant,the elutior s were stopped.

PART B.NITRATE Exmc'noN Fno vr Sntronrc Acm SoLU'noNs The final efliuentfrom each column, which was found to have a nit rate concentration ofabout 0,. 3 N in both cases, was placed in an individual 60 ml,cylindrical separator y funnel. Tov this aqueous solution in each funnelwas added 'ah'equivalent amount'of an extractantconsisting of a 0.2 Msolution of an amine in a kerosene diluent. (In the cases where thequaternary ammonium compounds were employed, since they are not solublein kerosene, chloroform was used as the diluent.) In lieu of keroseneother diluents may be employed such as chloroform talreadymentioned),benzene, toluene, xylene, heptane, light or heavy refined mineral oils,etc. The solutions inthe funnels were equilibrated by shaking themthoroughly and then allowing them to stand untilthe organic layerseparated out from theaqueous layer (or rafiinate) and was drawn off.The normality of the nitric acid in the raflinate was obtained andcompared with the concentration of nitrate which underwent the amineextraction treatment to determine the percentage of nitric acid whichhad been extracted. Tables LIV, which lists these percentages, will beseen to record the results of the tests when two ditferent amines ofeaeh type (i.e., primary, secondary, etc,) were employed. In eachinstance, it will be noted,'there is data for the column in which a 10%H 80 solution was utilized, and also data for the 20% H 804 solution, inorder to provide a basis for comparing the effectiveness of the presentinvention in separating nitrates from solutions having differentconcentrations of sulfates present.

Table I NITRATE EXTRACTION FROM SULFURIC ACID USING PRIMARY AIWINES' 1Mixture Nb. 1 indicates a com I ercially available mixture of aminesprincipallycorisisting oft'Gi.Hra'+iNHz Where 1z=12 to 15.

z. ixtu re N ,=2 indicates afcommerciallyavailable mixture of aminesTable III NITRATE EXTRACTION FROM SULFURIC ACID USING TERTIARY AIJINESHNO in Percent Amine H2804 HNOS Rafinatc HNO;

Extracted (10%) 2N. 0. 284 N 0. 085 70. l.

{(20% 4N 0. 310 N 0.086 72. a BDodecylbenzyl di-n- {(10%) 2N 0.284 N0065 77. 2 butyl (20%) 4N 0.310 N 0. 114 63. 2

Table IV NIIRATE EXTRACTION FROM SULFURIC ACID USING QUATERNARY AMMONIUMCOMPOUNDS HNOaiIl Percent Amine HaSOi HNO3 Raflinate HR ExtractedA-Dodecenyl trimcthyl {(10%) 2N 0.306 N 0. 000 100 ammonium chloride...(20%) 4N 0.310 N 0.000 100 B 3 {(10%) 2N O. 306 N 0.000 100 (20%) 4N;0.310 N 0.000 100 a Poly(metamethylparadodecylbcnzyl) dimethyl-y-(acrylamido) propylammonium chloride.

NITRATE STRIPPING FROM PRIMARY AMINES WITH BASIC SOLUTIONS Percent HNO:Stripped meq. of Base/meq. Amine BNO,

Amine Strippant erMimre 1 {823% 056%?1111:

1 Mixture No. 1 indicates a commercially available mixture of aminesprincipally consisting of t' -CuH2n-HNH2 where n=12 to 15.

2 Mixture No. 2 indicates a commercially available mixture of aminesprincipally consisting oi iI-C Hz +1NHg Where n= 18 to 24.

Table VI NITRATE STRIPPING FROM SECONDARY AMINES WITH BASIC SOLUTIONSPercent HNOa Stripped meq. of Base/meq. of Amine HNO:

Amine Strippant A Dodecylbenzyl tdodecylamine B Dodecenyl t 6 Table VIINITRATE STRIPPING FROM TERTIARY AMINES WITH BASIC SOLUTIONS meq. ofPercent Amino Strippant Base/meq. HNO:

of Amine Stripped HNO:

0.3N NH4OH 1. 5 84.3 Tfldmecmyl 0.3N NaOH 1. 5 72. a

Dodecylbcnzyl di-n-butyL- Table VIII NITRATE STRIPPING FROM QUATERNARYAMMONIUM a Poly(metamethylparadodecylbenzyl)dtmcthyl-y- (aorylamido)propylammonium chloride.

It will be noted from Tables LIV that values for percent HNO extractedare comparatively lower for the primary amines than for the others. Thisis due primarily to the solubility of the amine salts in the aqueousphase. As the equivalent weights of the amines increase the solubilitiesof the amine salts decrease and the nitric acid extraction increases.

It is of further interest to note that, although the quaternary ammoniumcompounds effected a 100% ex traction of the nitrate (Table IV), it wasnot possible to strip a sufiicient percentage of the nitrate for theamine to make recovery of the nitrate by this means commerciallyfeasible. However, this means of extracting nitrate from sulfuric acidsolutions is far more useful in any application where the main object isto extract the nitrate from nitrate-sulfate solutions, and there is noparticular requirement to salvage the nitrate as such. The quaternaries,moreover, have a special advantage over the other amines in that theycan extract the nitrates from neutral or alkaline solutions withouthaving to first make the system acidic.

The data in the above tables pertains to the separation of nitrates fromnitrate-sulfate solutions derived in the course of processing uranium bymeans of columns of ion-exchange resins. Such solutions are stronglyacid per se, and the extraction of the nitrate by means ofhigh-molecular weight amines in accordance with the present invention isthereby enabled to be carried out directly as described above. There aresome situations, however, where nitrate-sulfate solutions are obtainedwhich are essentially neutral. An example of this is in the so-calledResin-in-Pulp uranium recovery process (cf. The Resin-in-Pulp Processfor Recovery of Uranium, by R. F. Hollis and C. K. McArthur, a paperpresented at the International Conference on the Peaceful Uses of AtomicEnergy (Paper A/Conf. S/P/526 U.S.A. 6 July 1955). The solutions whichresult from that process (which up to now have had to be discarded incommercial practice) essentially comprise the following components(taken from an actual run which may be considered to be typical):

1.00 N Mg+++NH 1.54 N pH=6.8

Only a small percentage of nitrates can be extracted di- NEUTRAL NITRATE-SULFATE "SOLUTION ACIDIFI'ED BEFORE AMINEIS ADDED In theseexamples the amine, in so,= 1-1so, form, was employed to contact theaqueous solution 'whose components were listed above. The amine used wasan organic phase, 10% weight/volume (0.26 M) .dodecenyl t-dodecylamine,the same as in Table -II-B above.

. eq. Percent Vol. orig. V01. Amine/ N N03 in NO:

Aq. meq'. Raflinate Extracted Table X In these examples H SO wasadded'to'the neutral bleed liquor and a solution'of free aminein-kerosene was used to extract the HNO The amine used was an organicphase, weight/volume -(0.26"M) 'dodecenyl t-dodecylamine, the same as inTable H-B=above. The ratio meq. amine/meq. NO =1.03.

H+N N N05 in Percent Vol. org. -Vol. Aq. of Ag. Raflinate NOa ExtractedThe applications and data set-forth above'pertain to uranium processingoperations. 'Asearlierf mentioned, there is an equallyimp'ortantfield ofuse for the present invention in the salva'ging of nitrates-fromtrade-Wastes, as from nitration reactionsn (Zine example isin-connection with the-manufacture of nitrocellulose during which largequantities of water are us'ed-which become contaminated with nitric andsulfuric acids. 'ln one' plant. where from 2000to 10,000 gallons perminute of-acid waste water is reported (B. Dickerson-and -R. Brooks,Neutralization of Acid Wastes, 42- J. Ind. and Eng. Chem. 599, April-1950), to be discharged, itis estimated that from 100 to 500 tons-ofnitratearelost each day. By employment of the present invention, andrecycling the NHgOH' strippingsolution, itis'possible to take the'nitrate out as NH NO building it up to every large concentration. Toillustrate,-in-one case a 50% weight/volume ofammonium nitrate solutionwithsome added ammoniafwa's used' as a starter, and -i-t-wa's-foundinvention has made possible the recovery and,- re-use of expensivenitrates that otherwise would be lost as a res ult of having becomemixed with solutions" of sulfates in All that is necessary is to'acidify the" solu- 8 many industrial processes. This recovery iseconomically practical and the savings far outweigh the expense of thematerials, equipment and time-which'are required there for. From theexamples given it will be obvious that'the invention is capable of wideapplication. Further, it should "be apparent'that there may be employedas the extractant any high molecular weight amine, .assame. has hereinbeen defined, and not merely those which have herein been specificallymentioned for-illustrative purposes. Likewise, other bases besides thoseindicated: are suitable as the stripping agent. Because of this widelatitude with which our invention may readily be practiced by thoseskilled in" the art we believe it reasonable that we be not restrictedin coverage by virtue of any omissions from the foregoing specification,but only by the 'purviewmuie appended'laim's.

We claim:

1. A cyclic process for eluting uranium which has been I leachedfromdts' ore with sulfuric acid, filtered and--adsorbed onion-exchangeresin s,.and for recovering and reusing the nitrates used to elute .theuranium, said process comprising, first passing a nitric acid-ammoniumnitrate solution through the ion-exchange column whereby ions, nextcollecting the nitric acid eflluent from the sulfuric acid treatmentstep and mixing it in a separatory apparatus with a water insolubleamine from the group c'onsisting'of primary, secondary, and tertiaryamines, and quaternary ammonium compounds, each member'of' said grouphaving a molecular weight of at least 'about'185, whereby the nitricacid is adsorbedon the amine, 'then separating out the organic layer andmixing it witha base to form a nitrate salt solution, and acidifying theresulting solution with an acid selected from the group consisting ofnitric-and sulfuric acids-whereby to make thatsolution suitable forfurther use in elutinguranium frorn'ion-exchange resins on which it mayhave been adsorbed.

2. The process of claim 1 in which the amine is a mixtute ofiaminesprincipally comprising t.C H NH .in which n is a number taken from oneof two groups: 12" to 1.5:and 18 to 2 4.

3. The process of claim 1 in which the amine is dodgeylbenzylt-dodecylamine.

4. The process of claim 1 in which the amine is dodecenylt-dodecylamine.

5. The process of claim 1 in which the amine is tridodecenyl amine.

6. The process of claim 1 in which the amine is dodecenyltrimethylammonium chloride.

7. In a process for selectively extracting nitrates from a substantiallyneutral aqueous solution containg the following components: Cl,s N0 1Mg++;- NHJ, the step which comprises adding-;H S O in order to acidifythe solution prior to' the separation of the nitrates from the sulfatesby .equilibrating the solution with a waterinsoluble amine having amolecular weight of at least about 185.

8. In a process for selectively extracting nitrates from a substantiallyneutral aqueous solution containg the following components: (11%, N0 1S05, Mg++, the step which comprises adding H 304- in order toacidify awaterinsoluble amine having a molecular weight of at least about priorto'using it to separate the nitrates from thesulfates by equ-ilibratingthe solution with the amine.

9. A cycliclprocess for extracting nitrates from aqueous trade wastescontaining nitrates and sulfates, and building up the concentration"thereof, which process comprises, continuously mixing the ,aqueouswastes in a container of the sep-aratory funnel ",categoryjogether;witha waterinsoluble amine having a- "-molecular weight of atnleast about185', continuously separating -out--theorganic layer which comprises theamine having nitrates adsorbed thereon, continuously stripping thenitrates from the amine by mixing a nitrate-stripping solution of NH OHwith the organic layer to form NH NO and recycling the resultingsolution which contains NH OH and NH NO until the concentration of NH NOis built up to a desired level.

10. The process of claim 9 in which, after the nitratestripping solutionof NH OH is mixed with the organic layer to form NH NO' the solutionwhich results is fortified by the further addition of NH OH preparatoryto recycling it to effect further shipping of the nitrate from theamine.

References Cited in the file of this patent

1. A CYCLIC PROCESS FOR ELUTING URAMIUM WHICH HAS BEEN LEACHED FROM ITSORE WITH SULFURIC ACID, FILTERED AND ADSORBED ON ION-EXCHANGE RESINS,AND FOR RECOVERING AND REUSING THE NITRATES USED TO ELUTE THE URANIUM,SAID PROCCESS COMPRISING, FIRST PASSING A NITRIC ACID-AMMONIUM NITRATESOLUTION THROUGH THE ION-EXCHANGE COLUMN WHEREBY TO DISPLACE THE URANIUMON THE RESIN WITH NITRATE IONS AND MAKE POSSIBLE THE COLLECTION OFURANIUM IN THE EFFLUENT OF THIS STEP, THEN PASSING SULFURIC ACID THROUGHTHE COLUMN WHEREBY TO DISPLACE THE NITRATE IONS WITH SULFATE IONS, NEXTCOLLECTING THE NITRIC ACID EFFLUENT FROM THE SULFURIC ACID TREATMENTSTEP AND MIXING IT IN A SEPARATORY APPARATUS WITH A WATER INSOLUBLEAMINE FROM THE GROUP CONSISTING OF PRIMARY, SECONDARY, AND TERTIARYAMINES, AND QUATERNARY AMMONIUM COMPOUNDS, EACH MEMBER OF SAID GROUPHAVING A MOLECULAR WEIGHT OF AT LEAST ABOUT 185, WHEREBY THE NITRIC ACIDIS ADSORBED ON THE AMINE, THEN SEPARATING OUT THE ORGANIC LAYER ANDMIXING IT WITH A BASE TO FORM A NITRATE SALT SOLUTION, AND ACIDIFYINGTHE RESULTING SOLUTION WITH AN ACID SELECTED FROM THE GROUP CONSISTINGOF NITRIC AND SULFURIC ACIDS, WHEREBY TO MAKE THAT SOLUTION FOR FURTHERUSE IN ELUTING URANIUM FROM ION-EXCHANGE RESIN ON WHICH IT MAY HAVE BEENADSORBED.